This invention relates to thermally stabilized styrenic polymer-based thermoplastic formulations containing brominated cycloaliphatic flame retardants.
Styrenic polymers are usually classified as generalpurpose polystyrene (GPPS) or as impact modified polystyrene (IPS). GPPS is a high molecular weight (M.sub.w =200-300,000) clear polymer which is hard, rigid and free of odor and taste. It finds use in producing moldings, extrusions and films. IPS is a rubber-modified polystyrene which is characterized by its toughness and resistance to abuse. The rubber is dispersed in the polystyrene matrix in the form of discrete particles. IPS is not clear, but rather, is either translucent or opaque depending upon the amount of rubber used. The art recognizes two types of IPS, i.e., medium-impact polystyrene (MIPS) and high-impact polystyrene (HIPS), the former containing less rubber than the latter.
Styrenic polymers can be injection molded, extruded, thermoformed, etc. Also, styrenic polymer-based thermoplastic formulations can be prepared which incorporate blowing agents, such as pentane or hexane, to yield an expanded or a foamed product. Generally, the foamed product uses GPPS.
Both GPPS and IPS enjoy wide acceptance in the marketplace. With this acceptance has come many applications which require flame retardancy. One type of flame retardant recommended for use with GPPS and IPS is brominated cycloaliphatics, e.g., tetrabromocyclooctane and hexabromocyclododecane (HBCD). The HBCD is generally a mixture of solid HBCD isomers. The isomer identities and their amounts are determinative of whether the HBCD is a low-melt product having a melting point range within the range of from about 168.degree. C. to about 185.degree. C., for example a melting point of 172-184.degree. C., or a high melt product having a melting point range within the range from about 185.degree. C. to about 205.degree. C., for example a melting point of 185-195.degree. C. or a melting point of 200-205.degree. C. Other isomeric mixtures are possible to provide different melting points.
While brominated cycloaliphatics are excellent flame retardants, their presence in styrenic polymer-based thermoplastic formulations can cause serious color and/or viscosity problems if the thermoplastic formulations are exposed to the high temperatures which are used in some article or film forming techniques.